This application relates to a heat pump having a single expansion device coupled with a flow control device to properly route the refrigerant through the single expansion device dependent upon whether the heat pump is operating in a cooling mode or in a heating mode.
Refrigerant systems are utilized to control the temperature and humidity of air in various indoor environments to be conditioned. In a typical refrigerant system operating in the cooling mode, a refrigerant is compressed in a compressor and delivered to a condenser (or an outdoor heat exchanger in this case). In the condenser, heat is exchanged between outside ambient air and the refrigerant. From the condenser, the refrigerant passes to an expansion device, at which the refrigerant is expanded to a lower pressure and temperature, and then to an evaporator (or an indoor heat exchanger). In the evaporator, heat is exchanged between the refrigerant and the indoor air, to condition the indoor air. When the refrigerant system is operating, the evaporator cools the air that is being supplied to the indoor environment. In addition, as the temperature of the indoor air is lowered, moisture usually is also taken out of the air. In this manner, the humidity level of the indoor air can also be controlled.
The above description is of a refrigerant system being utilized in a cooling mode of operation. In the heating mode, the refrigerant flow through the system is essentially reversed. The indoor heat exchanger becomes the condenser and releases heat into the environment to be conditioned (heated in this case) and the outdoor heat exchanger serves the purpose of the evaporator and exchangers heat with a relatively cold outdoor air. Heat pumps are known as the systems that can reverse the refrigerant flow through the refrigerant cycle, in order to operate in both heating and cooling modes. This is usually achieved by incorporating a four-way reversing valve (or an equivalent device) into the system schematic downstream of the compressor discharge port. The four-way reversing valve selectively directs the refrigerant flow through indoor or outdoor heat exchanger when the system is in the heating or cooling mode of operation respectively. Typically, a pair of expansion devices, each along with a check valve, is employed.
One problem with the prior art heat pumps is the complexities associated with the provision of the expansion function. Since in the heat pumps the refrigerant will flow in opposed directions (depending on the mode of operation), it has been difficult to provide a single adequate expansion device. Additionally, since the requirements of enhanced reliability and improved control recently became one of the essential issues in the industry, thermal expansion devices are now frequently found in applications where fixed orifice expansion devices used to be a standard.
Another approach is disclosed in co-pending U.S. patent application Ser. No. 10/693,93, owned by the assignee of the present invention. In this concept, a single expansion device is utilized with a movable plunger that is moved to the appropriate position, depending on the mode of operation.
Another approach is to utilize an electronic expansion valve. However, electronic expansion valves are expensive and require additional electronics and sensors.